Does the Urban Environment Act as a Filter on the Individual Quality of Birds?

Agnès Saulnier,Josefa Bleu,Pierre Uhlrich,Sylvie Massemin,Gildas Lemonnier,Sandrine Zahn

doi:10.3390/birds3010007

Abstract

Phenotypic divergences of birds are common between urban and natural habitats and can result from different selective pressures between habitats or maladaptation to the city. No uniform patterns were observed, especially concerning markers of bird health, such as, for example, telomere length. Telomeres are involved in maintaining genome integrity and naturally shorten with age, but environmental stressors can accelerate their attrition. Thus, telomere length can be an indicator of individual quality. Some studies showed that urban breeders had longer telomeres than forest individuals. Two hypotheses can explain this result: (1) urban breeders are younger than forests breeders, and (2) cities act as a filter on individuals and only high-quality birds can successfully reproduce. In this context, we compared the age category (molting pattern) and morphological and physiological characteristics of urban and forest Great Tits before and during breeding. No differences in age or body condition were observed. However, urban breeders were smaller and had shorter telomeres than birds captured in winter. Urban birds had longer telomeres than forest birds, only in winter. These results highlight that urban habitats potentially favor smaller birds. However, the decrease in telomere length between winter and reproduction only in the city suggest a higher cost of reproduction in the city compared to the forest.

Highlights

IntroductionBirds 2022, 3 field [1,2]
Our study highlighted that urban individuals had a smaller body size than forest individuals, whatever the season, and that, for the urban site only, birds captured during breeding were smaller than birds captured during winter
The smaller body size of urban breeders compared to winter birds suggests that the urban environment would have a filtering role based on bird morphology, with a smaller size conferring an advantage regarding reproduction success, potentially since these birds are more agile or less prone to predation

Summary

Introduction

Birds 2022, 3 field [1,2] These optimized trade-offs between somatic maintenance and reproduction depend on individual capacity to exploit these resources [3]. Some individuals more efficient in resource acquisition are able to reduce the trade-off and allocate energy to both reproduction and self-maintenance, allowing high reproductive success while limiting the impact of reproduction on their survival [4,5]. These individuals are so-called of better ‘quality’, and will display a higher level of individual performance [5,6]. Heterogeneity in individual quality and performance will depend on environmental constraints

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